I recently bought a ”yoga mat” at a supermarket as the nights were a bit colder than I’d expected (early May in Greece). I don’t usually use a mat unless it’s cold.
Anyway it was just 140 cm (55”) long but felt fine (50cm wide, 6,5mm thick) and made a lot of heat difference.
Decades ago before Thermarest came out with their self inflating open cell foam pad, the norm for most backpackers and canoe campers was a 3/8 or 1/2 inch (9.5 to 12.5mm) closed cell foam pad for a sleeping pad. Commonly were even shorter than your yoga mat. No worries about puncturing them, but they got very stiff in cold weather, sometimes would crack in really cold weather.
Back then, air mattresses were either very heavy or puncture prone plastic sheeting.
I think this is the first time I heard someone speak highly of a 6.5mm yoga mat for a sleeping pad.